1. Field of Invention
The present invention relates to liquid crystal display (LCD) structures and methods of forming them. More particularly, the present invention relates to LCD structures of integrating a black matrix and a color filter into a substrate having a control circuit thereon and methods of forming the same.
2. Description of Related Art
Liquid crystal display (LCD) has many advantages over other conventional types of displays including high picture quality, small volume occupation, lightweight, low voltage driven and low power consumption. Hence, LCD is widely used in small portable televisions, mobile telephones, video recording units, notebook computers, desktop monitors, projector televisions and so on. LCD gradually replaces conventional cathode ray tube (CRT) as a mainstream display unit.
The main part of LCD is liquid crystal (LC) unit composed of two parallel transparent substrates and LC sealed therein. The mainstream of the LCD is thin film transistor (TFT) LCD. The fabrication processes of a TFT-LCD can be divided into four parts: TFT array, process, color filter (CF) process, LC cell assembly process, liquid crystal module (LCM) process.
The TFT array process is used to fabricate a TFT substrate. Each TFT respectively aligns with one pixel electrode. The CF process is used to fabricate color filter substrate. A color filter layer composed of different color filter sheet is on the color filter substrate, and a black matrix layer surrounds each color filter sheet.
The LC cell assembly process is used to parallel assembles TFT substrate and CF substrate, and bead spacers spread between them to maintain a fixed distance, i.e. cell gap, between TFT substrate and CF substrate. LC is injected into the cell gap then the injection opening is sealed. Basically, each pixel electrode is respectively corresponding to one color filter sheet, and the black matrix layer covers on TFTs and metal lines that connect different TFT.
The LCM process is used to attach a polarizer to a panel, and electrically connect driver IC and panel circuit. Then a reflector and a back-light are assembled on the panel. After a burn-in step, the LCM process is finished.
Generally speaking, the direction of liquid crystal molecule axes, which are controlled by TFT, determines whether each pixel is pervious to light or not. The color of each pixel is determined by the color of color filter sheet. For example, when light passes through a red color filter sheet, a red spot is shown on the panel. Mixing red, green and blue colors can show full-color images.
Since the molecular axes of liquid crystal molecules, which are between pixel electrodes and color filter sheets, have to be controlled precisely, the color filter and the TFT substrate must be aligned precisely. The tolerable error of alignment is only within several micron meters.
The heat coefficients of color filter substrate and TFT substrate are different, hence the precise alignment of pixel electrodes and color filter sheets is hard to achieve. Decreasing the product yield and increasing the production cost are caused by this problem. With growing size of substrates, the problem is getting serious. Therefore, light leakage and coin mura on panel is produced. But for increasing the size of black matrix to increase the alignment precision, the color contrast and brightness of LCD is decreased.
Another problem is the random distribution of bead spacers. The bead spacers may block some of the pixel area. Hence the aperture ratio of LCD is decreased. For smaller pixel area or for high-resolution panel, the problem is more serious.
An object of the invention is to provide a liquid crystal display structure, wherein a black matrix and a color filter layer both are on a control circuit substrate and pixel electrodes are on the color filter layer to increase the align preciseness of the color filter layer and the pixel electrodes. Besides, photoresist spacers are used to replace the conventional bead spacers to increase the brightness and color contrast of a liquid crystal display.
The liquid crystal display structure comprises a first substrate having a control circuit on it, and a black matrix layer, a color filter layer, a pixel electrode layer, a plurality of photoresist spacers, a liquid crystal layer, a common electrode and a second substrate are in turn on it.
A plurality of openings are in the black matrix layer to expose the first substrate. The color filter layer is composed of a plurality of color filter sheets aligning with each opening. Each pixel electrode aligns with each color filter sheet. The photoresist spacers are located on portions of areas covered by the black matrix, and their hardness is preferred to be about 2H to about 4H and their height is preferred to be about 1 to about 10 xcexcm. The photoresist spacers also can be composed of multi-layered color photoresist.
Another object of the invention is to provide methods of forming a liquid crystal display to increase alignment preciseness between color filter sheets and pixel electrodes, and photoresist spacers are used to replace conventional bead spacers.
Accordingly, in an embodiment, a black matrix layer is formed on a first substrate having a control circuit thereon. A plurality of openings are formed in the black matrix layer to expose the first substrate. A color filter layer is formed on the black matrix layer. A plurality of pixel electrodes are formed on the color filter to align with each of the openings. A plurality of photoresist spacers are formed on the first substrate to be located on portions of areas covered by the black matrix. The first substrate and a second substrate having a common electrode thereon are parallel assembled, wherein the photoresist spacers and the common electrode are between the first substrate and the second substrate. A liquid crystal layer is formed between the first substrate and the second substrate. The order of the step of forming the photoresist spacers and the step of the pixel electrodes can be exchanged.
In another embodiment, a black matrix layer is formed on a first substrate having a control circuit thereon. A plurality of openings are formed in the black matrix layer to expose the first substrate. A color filter layer is formed on the black matrix layer. A plurality of pixel electrodes are formed on the color filter layer to align with each of the openings. A plurality of photoresist spacers are formed on a second substrate having a common electrode thereon the first substrate and the second substrate are parallel assembled, wherein the photoresist spacers and the pixel electrodes are between the first substrate and the second substrate. A liquid crystal layer is formed between the first substrate and the second substrate.
A further object of this invention is to provide a method of forming a liquid crystal display, wherein multi-layered color photoresist are stacked to form photoresist spacers.
In this embodiment, a black matrix layer is formed on a first substrate having a control circuit thereon. A plurality of first, second and third openings are formed in the black matrix layer to expose the first substrate. A first color photoresist is formed on the first substrate. The first color photoresist is patterned to form a plurality of first filter sheets aligning with each of the first openings and a plurality of first spacers located on portions of areas covered by the black matrix. A second color photoresist is formed on the first substrate. The second color photoresist is patterned to form a plurality of second filter sheets aligning with each of the second openings and a plurality of second spacers overlapping with the first spacers. A third color photoresist is formed on the first substrate. The third color photoresist is patterned to form a plurality of third filter sheets aligning with each of the third openings and a plurality of third spacers overlapping with the second spacers. A plurality of pixel electrodes are respectively formed on the first, second and third filter sheets. The first substrate and a second substrate having a common electrode thereon are parallel assembled, wherein the photoresist spacers and the common electrode are between the first substrate and the second substrate. A liquid crystal layer is formed between the first substrate and the second substrate.
As embodied and broadly described herein, the invention provides liquid crystal structures and methods of forming the same, wherein the black matrix and the color filter are moved from the color substrate to the control circuit substrate. Since the alignment preciseness is mostly controlled by photolithography, the alignment error can be greatly reduced to below micron meter. Moreover, the photoresist spacers are located on portions of areas covered by the black matrix, the brightness and the color contrast of the liquid crystal display can be highly raised. Beside, the color photoresist is also used to form spacers, the production cost can be largely reduced and the production yield can be largely promoted.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.